OK - lets resume what conditional forwarders are. Usually when a DNS-Server is receiving a request from a client or himself , he's first checking if the request is for a name he's holding a zone for , then he's checking the cache, and if he's still unsucessfull he's forwarding the request to the IP-Adresses configured in the Forwarders-Tab of the Server Properties in the DNS-Managementconsole or dnsmgmt.msc. Therefore it was always quite tricky if you hold disjointed namespaces in your company (e.g. unix.example.com and windows.mycompany.org) but have not (enough) control over the parent namespaces. You usually had to resolve this by forwarders and secondary zones, or secondaries on both sides a.s.o. Read more at Ulfs Blog.